Portal 2 was set to have a new main protagonist but Valve found the original Aperture Science guinea pig too good to pass up a second time.
"We sort of agreed that as a character Chell was really successful in the first Portal," Valve's concept artist, Matt Charlesworth, explained to GameInformer.
"She fit into the world really well and complemented it without the distractions that a more flashy character would bring. She served a utilitarian purpose for that game, but at the same time when we started out on Portal 2 we weren't sure if we wanted to bring her back. So we explored a few other characters before returning to Chell."
He added: "Right from the beginning, we were constrained to replicate the character that was in the first game. Later on, we decided that we were probably missing a trick by not having Chell present, so we moved her back into that role."
Charlesworth went onto detail a number of design choices the developer made in bringing Chell back, including her nationality.
"We explored changing Chell's nationality for a little bit. Nobody really knew what Chell was in the first game. She kind of had a hint of Japanese ethnicity to her, but we were still not quite sure if we were going to keep her or make her a new character."
Earlier today, we posted concept art Valve released for Portal 2, showing new robots and the revamped Chell.